Process for producing olefins



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' ATTORNEY mama A 29, 1950 r PROCESS FOR PRODUCING OLEFINS William 0.Keeling, Mount Lebanon Township, Allegheny County, Pa., assignor toKoppers Company, Inc., Pittsburgh, Pa., a corporation of DelawareApplication June 14, 1944, Serial No. 540,248

Claims. (Cl. 280-683) This invention relates to a process for producinglight olefines, di-olefines, such as butadiene, acetylenes, andaromatics such as benzene, toluene, xylenes, and alkenyl aromatics asstyrene, vinyl naphthalenes, etc, More specifically, it relates to apyrolytic conversion process by means of which a wide variety ofhydrocarbon charging stocks can be converted into one or more of theseproducts in a new and novel manner.

This application is a continuation-inpart of my co-pending applicationSerial No. 597,692 filed March 9, 1932, Patent No. 2,363,532 issuedNovember 28, 1944 and covers improvements on the invention disclosed inthe parent application which was, broadly, a process for convertinghydrocarbons into motor fuels, unsaturates, aromatics, or fixed gases.whichever is desired, in which the charging stock is vaporized, thevapors further heated in a pipestill coil by indirect heat exchange andpartially cracked therein, and the conversion then completed by directlyadmixing the partially cracked vapors with a suitable heat-carrier gas.The total heat necessary for the conversion, therefore, is suppliedintwo stages by separate, independent supplies and oil-flowing of heatingmediums to permit separate and independent control of the heating donein each of the two stages and with the wasting of the spent heatingmedium used in the firststage. Thereby the quantity of heat-carrier gasrequired and used in the second, or direct, heating stage isreduced to asmall fraction of that. which would be required if only superheating ofthe vapors in the first stage were practiced, or if the total heat inputof the process were supplied by the heat-carrier gas in the directheating stage; as well as making possible the use'of separate heatingagents having different properties in each of the two heating stages.

One object of the present invention is the improvement of the processdisclosed in my co-pendingapplication Serial No. 597,692, whereby itbecomes more suitable for the production of selected primary reactionproducts by the pyrolysis of I quantities of methane and other lightsaturated hydrocarbons and heavy tar and/or carbon.

Another object of the invention is to provide a-novel method and meanswhereby the selected quantity of pyrolytic heat delivered and itseffective period of application to hydrocarbon charging stocks is madeeasily controllable within very narrow limits, so that there isrecoverable high yields of selected primary pyrolytic products such asacetylenes, ethylene, butadiene, butylenes, propylene and lightaromatics, and alkenyl aromatics, etc., with a minimum furtherconversion of desired products into unwanted products by secondarypyrolytic reactions.

The invention has for further objects such other improvements and suchother operative advantages or results as may be found to obtain in theprocesses or apparatus hereinafter described or claimed.

In prior processes for producing motor fuels,

the type of cracking employed may be termed digestive cracking becausethe charging stock, being converted, is retained in the reaction zonefor a period of time suflicient to permit the formation of not onlyprimary reaction products but also further or secondary reactions of, orbetween, the primary products. These secondary reactions consist offurther scissions of carbonto-carbon and/or carbon-tohydrogen linkagesin the primary products, alkylation, polymerization, and aromatization.These secondary reactions are highly desirable when producing motorfuels because they decrease the degree of unsaturation of the resultingmotor fuel and very materially increase its octane value. They are adisadvantage in that they very materially increase the amount of thecharging stock converted into hydrogen and saturated fixed gases,largely methane, and heavy ful oil or tar. Because of their nature, thefixed gases and tars are of little value for anything but fuel forheating purposes, The total amount of charging stock converted intomotor fuel, fixed gases, and tars and the ratio between the yields ofeach of these products depends largely upon the nature of the chargingstock and the cracking conditions. W. L. Nelson, on pages 315 to 319 ofhis book, "Petroleum Refinery Engineering," published by McGraw-Hill,first edition, gives a set of empirical equations for calculating theyields of these three products obtainable from any given charging stockby digestive cracking. It will be found from these equations, andconfirmed by other operating data in the literature, that the combinedfixed gas and tar yields from any given charging stock varies from about20% of very light charging stocks to about of very heavy chargingstocks. It is 3 thus readily apparent that the digestive type ofcracking is wasteful of the charging stock, at least insofar as itsconversion into useful and more valuable products, other than motorfuel, is concerned.

I have discovered that by adding certain steps, modirying others, and byoperating within certain limits with respect to temperatures and timeintervals, all of which will be described herein, the inventiondisclosed in the parent application, Serial No. 597,692, can be adaptedto selectively produce, from a wide range of charging stocks, maximumyields of ethylene, propylene, butylenes,

'amyienes and other oleiines, di-olen'nes such as butadiene, actylenes,benzol, toluol, xylenes, alkenyl aromatics, etc., all of which are badlyneeded for the production of various war materials such as syntheticrubber, IOU-octane aviation fuel, alcohol, explosives, etc. The neteffect of these modifications is to change the process disclosed inSerial No. 597,692 from a primarily digestive-type conversion process-toone. which for want of a more description term, will be called anexplosive-type of conversion process, from which the products obtainedare markedly different in character, being very largely primaryconversion products, as compared to the secondary conversion productslargely obtained by the digestive-type conversion.

The explosive-type cracking is characterized by the substantiallyinstantaneous application of a measured amount of heat energy suflicientonly to accomplish the pyrolytic conversion desired at a predeterminedtemperature level. This heat is applied to the molecules of the chargingstock which has already been heated just to, or above temperatures atwhich the atomic carbon-tocarbon and/or carbon-to-hydrogen linkagesbegin to rupture. The sudden application of the additional quantity ofheat causes substantially instantaneous rupture of the linkages of themolecules of the charging stock at their points of greatest weakness.The rupture is then followed by substantially instantaneous cooling ofreaction products to temperature levels at which no further primaryconversion can occur. I have found that by using this procedure, theproducts obtained are predominantly primary reaction products consistingprincipally of light unsaturates, suitable as starting materials in thesynthesis of various organic compounds and a relatively small amount oflight, liquid products containing a large percentage of benzene,toluene, xylenes, and some naphthalenes and anthracenes, but little, ifany, heavy tar. Furthermore, I have found that I can vary the yield ofany given unsaturate or aromatic by varying the temperature levelsemployed for the conversions and by careful control of the temperaturedifferential between the superheated vapors of the material to beconverted and material carrying the heat energy required for theconversion.

Although I use the preferred explosive-type of cracking for theproduction of primary products, I have found that when cracking tobutadiene, a small amount of acetylenes are also formed. Theseacetylenes are very troublesome in the subsequent butadiene purificationsteps and, unless removed, seriously affect the properties of the synthetic rubber made therefrom. It is of advantage, therefore, to eitherprevent acetylene formation or to hold the quantities made below certainlimits. Owin to the nature of pyrolysis, it is impossible to preventacetylene formation at the temperatures required for butadieneproduction.

4 But I have found that if a limited digestive period follows theformation of the primary products, the quantities of acetylenes formedcan be reduced by as much as a half. This digestive period will normallyvary from about a third to twice the time interval required for thecompletion of the desired primary reactions, depending on the digestiontemperatures employed. Experiments indicate that if this digestionperiod does not exceed approximately 0.2 second, the loss of primaryproducts, other than acetylenes, and the increase in tar formation willbe negligible. Then immediately following the digestion step, thereaction products are quenched to temperatures at which no furtherthermal reactions can occur.

The following table shows the effect oi this limited digestive period,following the cracking period, upon the acetylenes content of theproducts made when cracking cyclohexane at various temperatures.

a n Wt? Reaction m a Time Acety enos Temp Second: in Reaction Products1, son o. 00 a. o 1, son 0. 178 1. 1 1, 875 o. 00 a o l, 875 0. 123 1. 21, 876 0. 184 1. 0 1, W) 0. 060 3. 0 1, 900 0. car a 1 1, 9&0 0. 0o 2. 81, 950 0. 117 1. 7 1, 950 0. 131 1. 6 7, (I!) 0. 043 5. 5 2, 000 o. 0002. 1

But where the production of acetylenes is desired, no digestive periodis to be used. Instead, high reaction temperatures and short reactiontimes are preferred.

According to the present invention, the total heat requirements for thedesired conversion is applied in two stages. In the first stage, part orall of the charging stock, depending on its composition, is vaporizedand the resulting vapors are then further heated very rapidly totemperatures at which the hydrocarbon molecules become unstable or evenbegin to decompose, but with this diflerence over the prior art. Suchdecomposition, or cracking, as may occur is confined to primarypyrolytic reactions and preferably to scission of cabon-to-carbonlinkages. In the case of pure hydrocarbons, such as cyclohexane, orlight mixtures such as natural gasoline or light naphthas, the maximumyields of certain desired products such as butadiene will be obtained bybringing the charging stock only to the point of molecular instabilityin this stage and confining the explosive, or substantiallyinstantaneous, disruption of the molecules to the second stage underconditions to be described later.

In the case of heavy hydrocarbon mixtures such as gas oils or residualoil charging stocks, the reactions in the first stage are confined toprimary pyrolytic reactions by means of which the boiling point range isnarrowed and the thermal stabilities of the hydrocarbons in the stockare made more uniform by primary cracking of the heavier and more easilycracked hydrocarbons. The charging stock now rendered more uniform as toboiling point and thermal stability will yield more nearly the sameproducts when subjected to the much more severe explosive-typedisruption in the second stage. I have found that this preliminarytreatment oi-the charging stock can be confined to the production of asuitable. predigested charge for the second conversion stage by caryingout the treatment in the first stage in such a manner that any normallygaseous conversion products formed thereby will contain not more than10% and preferably not more than by weight of methane. The heating isdone very rapidly by indirect heat exchange in pipestill coils, out ofdirect contact with the heating medium and confining such primarycracking as occurs to the production of primary cracked productsequivalent to not more than approximately 40% of the total crackingoccurring in both the first and second conversion stages. Such aprocedure keeps to a minimum the yields of unwanted hydrogen, methaneand tars from the charging stocks. I I have found that for the maximumproduction of any particular product from a given charging stock,careful control of reaction temperatures and times used in theconversion reaction mustbc practiced, as well as the maintenance ofdefinite relationships between the temperatures of the vapors leavingthe first conversion stage, the average conversion temperature, and thetempertaure of the heat-carrier medium prior to the latter's admixturewith the vapors from the first conversion stage.

For the production of heavy unsaturates such as butylenes, amylenes,etc., reaction times of approximately 0.2 second, or less, are used withan average reaction temperature ranging from 1300 to 1500 R, dependingon the stock being cracked. For the production of butadiene atemperature range of 1400 to 1550" F. should be employed over a timeinterval of 0.2 second, or less. For the production of ethylene,conversion temperatures of 1500 to 1700 F. over a period of 0.2 second,or less, should be used. For the production of aromatics, a temperaturerange about the same as that used for ethylene production is best, butsomewhat longer periods of time should be used. For the production ofstyrene from ethylbenzene or vinyl-naphthalene from ethyl-naphthalene, atemperature range of 1350 to 1650 F. is required over atime interval notexceeding 0.2 second. There appears to be no definite optimumtemperature range for the production of .acetylenes as they begin toappear at about 1300 1". and progressively increase in quantities up toa temperature of about 2200 F. But the time interval should be less thanapproximately 0.2 second and preferably less than 0.1 second.

For the maximum yields of desirable products from a given, chargingstock, it is necessary to hold to a minimum the amount of the stockconverted to the undesirable hydrogen, methane, and tar, or even carbon.I do this by close control, or the maintenance of definite relationshipsbetween the temperature of the vapors leaving the first conversionstage, the mean temperature utilized in the second or direct heatingconversion stage. and the temperature of the heat-carrier medium justprior to its admixture with the vapors from-the primary conversionstage. As the vapors leave this latter stage, they are at, or above, thetemperature at which rupture of the carbon-to-carbon and/orcarbon-to-hydrogen linkages begins. Consequently, the hydrocarbonmolecules are very sensitive to thermal shocks. And if the shock is tooviolent, as when using too high temperatures in the heat-carrier medium,a considerable number of the molecules break down completely tohydrogen, methane,

Q and carbon. I have found that best results are obtained when the ratioof the diflerence in temperature between the heat-carrier medium and themean temperature used in the direct conversion stage and the differencebetween this mean conversion temperature and the temperature of thevapors leaving the primary conversion stage is not less thanapproximately 1 to 1 and not more than approximately 2 to 1.

By carrying out the conversion reactions of the second stage in aheavily insulated chamber, the conversion takes place therein withoutloss of heat from the reaction chamber. Since most, or all, of theprimary conversion reactions are endothermic, this means that as heat isconsumed by the reactions, the temperature of the reaction mixture willdrop, due to the decrease in sensible heat remaining in the mixture. Ihave found that this fact can be utilized when the reaction products aresusceptible to further decomposition at the highest reactiontemperatures, by supplying substantially instantaneously only sufiicientheat to carry out the desired reactions to a predetermined degree ofcompletion. When that point has been reached, the temperature of themixture has dropped sufilciently to protect the reaction products. Thequantity oi. heat supplied is regulated by the temperature and volume ofthe heat-carrier gas used. A good illustration of the procedure can begotten from the following table and Figure 1, containing data obtainedwhen cracking cyclohexane to butadiene with superheated steam whenadmixing the steam substantially instantaneously with cyclohexane at asingle point of admixture.

Temp. steam, F 2, 019 2, 013 1, 900 Temp. cyclohexane vapors, F 1,0821,085 l, 115 Temp. mixture entering reactor, "F l, 416 l, 497 l, 360Temp. mixture leaving reactor, F 985 1, 000 913 Theoretical maximummixture temperature,

l, 800 1, 565 Mo] ratio steam to cyclohexane 11.8: l 23. 7:1 13.6:1Contact time, Seconds 0. 060 0. 04 3 0. 000 Percent conversion per pass3i. 2 61. 8 20. 0 Ultimate Molar Yields in Per cent of Theoretical:

Butadiene 56. 5 47. 1 60. 7 Ethylene. 89. 6 99. 0 Hydrogen 123. 4 87. 5

The theoretical primary products of the thermal decomposition of 1 molof cyclohexane are 1 mol of butadiene, 1 mol of ethylene, and 1 mol ofhydrogen. But butadiene is susceptible to further conversion at hightemperatures and long reaction times, hence it should be protected fromfurther conversion, after it is formed, by a re-- duction of thereaction temperature to levels at which it is relatively stable. FromFigure 1, it

will be seen that about 76% of the available heat supplied forconversion is absorbed in the first 50% of the length of the reactionchamber. This means that substantially 76% of the total conversionoccurs in the first half of the allotted reaction time and that duringthe remainder of the time only 24% of the primary conversion of thecyclohexane occurred plus such secondary conversion of the butadieneproduced as the resulting temperature permits. Inspection of the tableshows that if the temperature and quantity the calculated temperaturesof the mixtures of heat carrier gas and charging stock vapors afteradmixture is completed but before any cracking occurs. It is calculatedfrom the weights of vapors and heat carrier gases entering the mixture,their temperatures before admixture and their specific heats. Because asmall but definite time interval is required for complete admixture andbecause some cracking of vapors occurs befor admixture is completed, anymeasured mixture temperature will always be lower than the theoreticalmixture temperature by an amount corresponding to the sensible heat ofthe mixture absorbed by the endothermic heat involved in the crackingreaction which has already occurred up to the point in the reaction zonewhere the temperature measurement is taken.

The more nearly instantaneous is the mixture of the vapor and heatcarrier gases, the more nearly the measured mixture temperature willapproach the theoretical maximum mixture temperature.

Thus the table shows the actual yield obtained by cracking as comparedwith the theoretical calculated yield. In other words the table showsthe amount of heat available for cracking which was supplied atpredetermined temperature levels and the yield of products obtained bycracking.

In another embodiment of the invention, the heat-carrier gas is rapidlyadmixed with the superheated vapors to be converted at more than onepoint, allowing a substantial degree of the desired conversion to occurbetween each successive point of injection. The temperature of theheat-carrier gas admitted at each point may be the same. Or thetemperature of the heat-carrier gas at any one point of admixture maydiffer from that at any other point of admixture.

By way of illustration only, sufiicient heat-carrier gas is admitted atthe first point of admixture to supply suflicient available heat toraise the temperature of the reaction mixture to the desired reactiontemperature level plus an additional amount sufiicient to cause, sayhalf of the desired primary conversion and then at the second point ofinjection, sufilclent additional heatcarrier gas is injected to providethe quantity of available heat necessary to complete the remainder ofthe desired primary conversion. It is to be understood, however, that Ido not wish to limit myself to two successive points of injection ofheat-carrier gas nor to the accomplishment of any fixed amount ofprimary conversion after each point of admixture, for the number ofpoints of injection and the amount of conversion accomplished after eachpoint of iniection will vary with the type of charging stock processedand conversion products desired. By means of this embodiment of theinvention, it is possible to maintain more nearly uniform the optimumtemperature level for the production of any desired conversion productthan could be accured by use of a single injection point. It makespossible the supply of a greater quantity of available heat for anydesired conversion without raising the temperature of the vapors to beconverted to a temperature so high that undesirable primary conversionoccurs, such as excessive disruption of the molecules of the chargingstock to hydrogen, methane. and carbon, or other undesirable products.It makes possible the maintenance of the optimum diiferentials betweenthe temperature oi the vapors to be converted and the heat-carrier gas,prior to admixture, without at the same time unduly limiting thequantity of available heat which can be supplied for desired conversionreactions. In other words, it makes possible greater yields of desiredproducts per pass where recycle operations must "be used, as well as thegreatest possible yields of desired products where single pass operationis to be employed.

When using the invention for the production of actylenes or other highlyunsaturated products, yields may be enhanced by the introduction ofany-suitable oxidizing agent into the heatcarrier gas, prior toadmixture with the vapors to be converted, or into the stream ofpartially converted hydrocarbons at a point subsequent to the firstadmixture of said vapors and heatcarrier gas. Such an oxidizing agentshould not exceed, in amount, the equivalent of 0.5 mol of free oxygenper mol of hydrocarbons to be converted. By oxidizing agent is meant anysubstance capable of removing hydrogen atoms from the molecules of theconversion products.

Precise control of reaction times is obtained by carefully proportioningthe free space of the reaction chamber to the volume of vapors and gasesto be passed therethrough, so that the vapors and gases can remain inthe chamber for only the desired time interval.

For substantially instantaneously quenching, or arresting the progressof conversion in the materials leaving the second conversion stage, Iprefer'to inject a spray of a liquid which can be easily separated fromthe final conversion products and which will introduce no extraneousimpurities into these products. Two examples of such desirable quenchingagents are water and light previously formed distillates made by theprocess. When operating on low boiling charging stock to produce lowboiling products, I ordinarily prefer to use water as the quenchingagent and then immediately further cool the reaction products by passingthem through a washbox such as is used in the manufactured gas industryin the manner shown diagrammatically in Figure 2. When operating on highboiling charging stocks where part of the products are also highboiling, it sometimes is of advantage to quench, with either water or apreviously formed distillate, to temperatures of 400 to 700 F.,scrubbing out the highest boiling conversion products with a suitableheavy oil and then further cooling to condense and absorb the remaininghigh boiling conversion products to separate them from the fixed gases.or lightest conversion products, in the manner shown diagrammatically inFigure 3.

Where maximum yields of any particular product is desired, thoseportions of the conversion products of lesser value and suitable forfurther treatment, after separation from the desired products, may berecycled for further conversion.

The method of separation of desired products from the rest of theconversion products will depend upon the particular properties of thedesired products. In general, the methods used will be fractionaldistillation, liquefaction followed by fractional distillation,treatment with selective solvents, or any other well known means.

Appended to these specifications and forming a part thereof are drawingsof which:

Figure 1 presents a graph showing the rate of heat absorption above aselected temperature level by primary thermal reactions, when crackingcyclohexane to butadiene, as the reacting I for insuring substantiallymixture progresses through a reaction chamber in which it resided for atotal of 0.08 second;

Figure 2 presents a schematic flow-diagram of one modification of theinvention in which superheated steam is used as the heat-carrier gas andin which single-point injection of the heat-carrier gas is practiced;

Figure 3 presents a, schematic flow-diagram of another modification ofthe invention in which combustion gases are used as the heat-carrier gasand in which two-point injection of the heatcarrier gas is practiced.

Referring now to Figure 1, there is disclosed a graph depicting thepercent of the required conversion heat absorbed, above a giventemperature level, plotted against the percent of the total length ofthe reaction chamber at which the absorption occurred. In the particularcracking run, during which the measurements were made, the totalreaction time was 0.08 second. The curve shows that the rate of heatabsorption in approximately the first 30% of the reaction chamber isvery rapid and that as the conversion mixture nears the end of thereaction chamber,

.the rate of heat absorption, which is a measure of the amount ofconversion occurring, rapidly decreases until in the last of the lengthof the chamber, a negligible amount of conversion occurred. Thisillustrates very forcefully the self-quenching feature of the inventionas described above. It also illustrates very forcefully the absolutenecessity of providing suitable means instantaneous and thoroughadmixture of the oil vapors and heatcarrier gas. 1 were obtained fromthermo-couple readings of temperatures at a. series of pointsdistributed along the length of the axis of the reaction chamber.Samples of the mixture of oil vapors and heat carrier gas were takenfrom the reaction chamber axis atpoints adjacent the points where thethermo-couples were located.

Referring now particularly to Figure 2, there is disclosed amodification of the invention in which single-point injection of theheat-carrier gas is practiced. Steam is shown as the heatcarrier gasalthough any other inert gas could be used. The charging stock is pumpedthrough .vaporizer coil 6, located in pipestill l, and heated to itsboiling point, or above. If the stock contains heavy fractions,undesirable as cracking stock, the heated stock passes through valve 1,valve 32 being closed, into evaporator 2 where the lighter, desirablecharging stock is vaporized and the vapors separated from theundesirable .heavy fractions remaining in the liquid phase, and theseparated vapors pass through valve 34 into the cracking coil 9. Theliquid residue is withdrawn from the evaporator through valve II. Ifthe-charging stock is of narrow boiling point range and it allconstitutes a desirable cracking stock, the entire stock may bevaporized in coil 6 and the vapors pass through valve 32 and into line33 into cracking coil 9, valves I and it being closed.

While passing through cracking coil 9, the vapors are heated to, orabove, the temperature at which the hydrocarbons become unstable, but

The points on the curve of Figure flu any cracking occurring therein isconfined to the bility, not more than approximately 5% by weight of thestock should be converted into products boiling below the initialboiling point of the original charge and no substantial amount ofmaterials should be formed boiling at a temperature higher than the endpoint of the original charge. If heavy charging stocks are to bepartially cracked in coil 9, the same procedure is followed except thatthe fixed gases formed should preferably not contain more than 10% byweight of methane and no substantial amounts of products having a higherboiling point than the end point of the portions of the originalcharging stock passed, as vapors, through the coil.

The oil in coil 6 and vapors in coil 9 are heated by indirect heatexchange with hot products of combustion formed in the combustionchamber of the still and by radiation from the burning fuel, but no partof the combustion gases formed in the still ever come in contact withthe oil or its vapors.

The heated oil vapors leave cracking coil 9 and enter the mixingchamber, or zone III, which, in this case, is shown as the throat of aVenturi tube. At this point, the heated vapors are thoroughly andsubstantially instantaneously admixed with the heat-carrier gas frompipe 20. For proper mixing, the heat-carrier gas and oil vapors shouldmix by means of turbulent flow in the mixing zone and the velocity ofapproach of the vapors and ga es to the mixing zone should be such thatneither nters the mixing zone as a jet strong enough to interfereseriously with or destroy turbulent fiow in the mixing zone. It is to beunderstood, however, that any other suitable means for insuringsubstantially instantaneous and thorough admixture and turbulent flowmay be used.

The mixture of heat-carrier gas and oil vapors is discharged from themixing zone l0 into the reaction zone 4, through which they continue tomove by turbulent fiow. In this modification, the reaction zone consistsof the diverging cone of the Venturi tube. and is of such length as toprovide the precise time interval required for the completion of theprimary thermal reactions desired above the temperature level at whichthe conversion products leave the reaction chamber. Both the mixing andreaction zones are housed in a heavily insulated structure so that allther-: mal reactions occurring therein without loss of heat byconduction or radiation from the reaction chamber.

The conversion products are" discharged from .box 5, such as is used inconventional water-gas machines. The quench water can be partly freshwater supplied to pump 29 through line 30 and partly used water drawninto pum 29 from the wash-box. The water is forced through line 3| andthrough the sprays 26, for quenching the reaction products. As a safetymeasure against failure of the float 35 and valve 28, an adjustable,vented syphon water level controller 21 can be provided to prevent thewater level from ever exceeding a predetermined maximum level. Thetemperatures maintained in the wash-box are such that the desiredconversion products remain in the vapor phase and pass out of thewash-box through pipe 24 to conventional final coolers and separatingequipment not shown. The heavier products condensing in the wash-boxaccumulate on the surface of the water and are withdrawn asaaisa througha superheater where it is heated to the desired temperature. If desired,coil llcan be eliminated from the pipestill and the steam passeddirectly into the-superheater. The superheaters used for illustrationare shown as blast furnace type stoves s and I, but any other meanscapable of heating the steam to the desired temperatures may be used. Inorder to operate continuously, two or more blast furnace type stoves areprovided, so that while steam is passing through one stove, the other,or others. are being ilred to store up the necessary heat in theircheckerwork. As shown, steam leaving coil ll passu through valve ll,valves I1 and "being closed, into stove l and thence through valve l8and lines 25 and 20 into the mixing zone ll. When the temperature of thesteam leaving stove 8 falls below the required level, valves I! and IIare closed and valves l1 and II are opened and the steam from coil llnow passes through valve ll into stove I and out through valve II andlines fl and ii into the mixing zone It. To maintain the temperature ofthe steam, entering the mixing zone ll, constant, a portion of the steamleaving coil it is by-passed around the stoves through valve l4 and linell into line II. The amount by-passed is that necessary to keep thetemperature of the highly heated steam, ml; the stoves, at thetemperature level de- Ifanoxidizing gasistobeusedforsecuring a greaterdegree of unsaturaticn in the conversion products, a suitable oxidizinggas is admitted through valve l2 into the steam passing to thesuperheater coil II and blast furnace stoves l and I. It is to beunderstood, however, that if superheating of the oxi l s gas isunnecessary or undesirable, said gas can be introduced into the steam atthe mixing zone ll or any point in the steam supply system priorthereto.

Although steam, heated in blast furnace stoves, has been shown as theheat-carrier gas, it is to be understood that I do not intend to limitmyself to this particular combination. For any inert gas, heated in anymanner to a suitable temperature, could be used. If combustion ases arepreferred, they may be generated and tempered in the manner shown inFigure 3.

Referring now to Figure 3, there is discloud a modification of theinvention in which combustion gases are used as the heat-carrier gas andin which two-point injection of the heat-carrier gas is practiced, butit is to be understood that any suitable heat-carrier gas may be usedwith suitable changes in equipment for producing or heating such gases.The charging stock is picked up by pump 31 and forced through vaporizercoil 38, I

located in pipestill a, and into evaporator ll where the vaporizedfractions are separated from any liquid residue remaining. The residueis withdrawn from the evaporator through valve 41 and can be withdrawnto storage or can be sent to the scrubber ll through pipe 42, by meansnot shown, for use as a scrubbing menstruum.

The vapors released in evaporator ll leave that 13 1vesselthroushpipeuand assthroughmc i l coil ll, located in pipcetill It.in which the vapor! are rapidly heated to temperatures at which primaryconversion begins but for a length of time which prevents more thanapproximately 40% of the total amount of conversion from occurring inthe coil ll.

The partially converted vapors from coil ll are injected into a rapidlymoving stream of part of the heat-carrier gas at point ll, just prior toan abrupt change of direction of flow of the resulting mixture, toobtain thorough admixture, and thenpasses throughtheilrstpartcf thereaction chamber 48. where the selected. portion of the primaryconversion is accomplished, and thence through the throat of the Venturitype mixer 44, where the partially converted hydrocarbons are admixedwith the remainder of the heat-carrier gas. The resulting mixture thenpasses into the diverging cone ll of the Venturi mixer which serves asthe second part of the reaction chamber ll and in which the remainder ofthe desired primary conversions occur.

The reaction mixture is then discharged into stand-pipe It in which itis quenched or shockchilled to approximately 500 F. by a spray of quenchliquid introducedthrough pipe II.

The cooled vapors, and any condensate formed by the cooling, aredischarged from the standpipe directly into the lower-part ofscrubberll, in which the vapors are counter-currently scrubbed with a heavy oilfor removal of high.

boiling conversion products, tars, etc. The nature and amounts of thehigher boiling conversion products passing from the scrubber with thegas and lighter conversion products can be regulated in the well knownmanner by the temperature and amount of scrubbing oil introduced intothe scrubber through pipe I! and the amount and temperature of thatrecycled from the base of the scrubber through pump it, cooler l4, andpipe ll, back over the top trays of the scrubber. Surplus scrubber oiland heavy condensate are withdrawn from the scrubber through valve IIand sent to fuel oil storage or disposed of otherwise. The coolingmedium used in cooler N can be any suitable material. One example wouldbe part, or all, of the fresh scrubbing oil to be introduced throughpipe I! in bringing it to the proper temperature for introduction ontothe top trays.

The gases and vapors leaving the scrubber can either be passed throughcooler I by opening valves II and II and closing valve It or can bepassed through the by-pass around the cooler by opening valve It andclosing valves '0 and I, depending upon the stock being cracked and theproducts made. The products passing through or around the cooler 51 flowthrough a line a to the base of the direct cooler ll. If heavy aromaticsor strongly emulsifying products are being made or where the smallestpossible volume of cooling agent is to be circulated through directcooler ll, then cooler II can be used. Or if it is desired to do all thecooling of the products in the direct cooler, cooler IT can beby-passed. The gases and conversion products are discharged into thebase of the direct cooler II where they are counter-currently cooled andwashed with a suitable menstruum, introduced through pipe 02, condensingor absorbing the hydrocarbon products, boiling above a predeterminedtemperature, by regulating the temperature and volume of the washingmenstruum used, in the well known manner.

The wash menstruum, together with any condensate, water and dissolvedhydrocarbons gravitate to the bottom of the direct cooler collecting ina pool in the base. An indirect heating coil may be submerged in thepool of liquid to heat the collected oil to a temperature sufficientlyhigh to expel the highest boiling hydrocarbon it is desired to carry outof the cooler in the fixed gases. The liquids, forming a seal in thebase of the direct cooler, are withdrawn from the cooler through theoverflow syphons 63, having a vent 84 for breaking the vacuum, or by anyother suitable device, to an oil-water separator where any water isseparated from the oil and discarded and the oil is then separatelyprocessed to recover any desired conversion products it might contain byany suitable means, not shown. I

The fixed gases, containing the lighter conversion products, pass fromthe direct cooler through valve 65 and pipe 68 to suitable equipment,not shown, for separating therefrom any, or all, of the lightestconversion products it might be desired to recover.

In this modification of the invention, combustion gases are shown as theheat-carrier gas used, although it is to be understood that withsuitable apparatus modification any other suitable gas might be used,such as steam as in the modification disclosed in Figure 2.

Air for combustion is compressed and stored in air tank 81. The pressuremaintained in this container is greater than the pressure maintained inthe conversion system by an amount necessary to force the air from thecontainer through the inspirator, to draw in the fuel gas and dischargethe air-fuel mixture into the combustion zone against conversion systempressure. This pressure differential is maintained by a suitable loadingof the diaphragm-type throttle valve 88. placed in pipe 89 between theair tank 81 and inspirator 10.

Fuel gas is compressed and stored in gas tank H. The pressure maintainedin this container is substantially the same as the pressure maintainedin the conversion system.

Air .is drawn through valve I2 by compressor 18 and discharged into airtank 61. As long as the pressure in this container remains at aconstantdifferential above that maintained in the conversion system, this inletvalve I2 remains open. As soon as the pressure in air tank 81 begins toexceed the proper differential, the diaphragm begins to close valve 12so that the air supply to the compressor is reduced or even cut off. Assoon as the air pressure in the tank drops to the proper differential,the valve begins to open up. In this fashion, the air supply in thecontainer is maintained constant at constant pressure.

Fuel gas is drawn through a diaphragm-type valve 14 by compressor I5 anddischarged into gas tank I I. Pressure in this tank is maintainedconstant at substantially conversion system pressure by means of adiaphragm-type throttle valve I8 placed in gas line 11 between the gastank and inspirator I0. If the pressure in the gas tank 14 side of thediaphragm is maintained at the pressure of the air tank II by means ofline 98.

By thus maintaining the air and gas supplies at constant pressures andby use of a properly sized orifice in the gas line at the inspirator,the air-fuel-gas mixture supplied to the burner is constantlyproportioned, regardless of any pressure changes in t e conversionsystem. Hence the .combustion gases formed will have a uniformcomposition regardless of any pressure changes in the conversion system.Conversion system pressures are communicated to the control valvesthrough pipe 18 and its branches I9, and II.

The air-fuel mixture is discharged through pipe 82 into the burner,preferably a surfacecombustion type placed in the insulated duct 88where combustion is rapid and complete. The combustion gases formed aretoo hot to directly admix with the hydrocarbons to be converted, forreasons stated above. They are, therefore, first cooled by admixturewith a cooler gas; such as steam, admitted through valve 84 in pipe 88.In order to maintain a uniform heat-carrier gas temperature, thequantity of the cooler gas admitted is regulated by thermostatic controlof valve 84. A thermostat 86, placed in the path of the temperedcombustion gas, actuates the mechanism of valve 84 so that the latterwill admit only sufllcient cooler gas to maintain constant thetemperature at which the thermostat is set.

The tempered heat-carrier gas leaves duct 88 through two orifices 81 and88 and enters the reaction chamber 43 for admixture with thehydrocarbons to be converted. These orifices are so sized that theproper amount of heat-carrier gas is admitted through orifice 81 toaccomplish the portion of the conversion desired in the first part ofthe reaction chamber, and'through 88 to complete the conversion in thesecond part of the reaction chamber.

If an oxidizing agent is to be used to obtain a greater degree ofunsaturation in the conversion products, it ean'be introduced as excessair' used for combustion, or with the tempering gas introduced throughvalve 84 and pipe 85. But I find thatbetter results are obtained if theoxidizing agent is introduced after the formation of at least part ofthe unsaturated primary conversion products. For this reason, I preferto introduce the oxidizing agent through valve 89 into that portion ofthe heat-carrier gas passed through orifice 88 and used to complete theconversion.

If heat-carrier gas at different temperatures is to be used at thevarious points of admixture, such gas may be separately generated andtempered for each point of admixture, in a manner similar to that shown,or in the manner shown by passing a portion of the tempering gas in pipethrough valve 98 into the stream of heatcarrier gas passing throughorifice 81, at the point 91 situated between the orifice 81 and thepoint 80 at which the hydrocarbon vapors are introduced. a

For illustrating the results obtainable when practicing the invention,the following data, de-' termined by laboratory and pilot plantoperations, are cited as specific examples.

.The first set of data illustrates the influence of the differentialbetween the temperature of the heat-carrier gas and the superheatedhydrocarbon vapors when cracking substantially pure cyclohexane tobutadiene and ethylene as well as the desirability of superheating thevapors to incipient cracking beiore admixture with the heatcarrier gas.I

It is to be understood that the temperature at which the weakestcarbon-to-carbon linkage of cyclohexane starts to rupture is in thevicinity of 1100' 1". Example 3 shows clearly the advantage ofsuperheating the cyclohexane vapor to 1100' before finishing thecracking with the heat-car- Thus the above table shows the actual yieldobtained by cracking as compared to the theoretical calculated yield. Inother words the table shows the amount of heat available for crackingwhich was supplied at predetermined temperature levels and the yields ofproducts obtained by cracking.

The next set 01 data illustrates theini'iuence of the differentialbetween the temperature of the heat-carrier gas and the superheatedhydrocarbon vapors and the influence of conversion temperature upon theyields of various conversion products from petroleum hydrocarbons withsingle pass operation. It also shows that the selection of chargingstocks is not without intluence on the yields of certain conversionprodnote. In the following tables the diflerent mean conversiontemperatures are due to the diflerent volumes of carrier gas which weremixed with the hydrocarbon vapors for cracking. In column I is shown theexcessive volume of methane formed and the high carbon loss due toexcessive temperatures which cause secondary reactions.

10 version products having greater molecular weights than that ofpropylene, but after the removal of benzene, toluene. xylene, and tar.

Ultimate yields of ethylene obtained by Tet-1 1W The foregoingdescriptions are merely illustrative of two modifications or myinvention, but it is to be understood that various changes andalternative arrangements may be made within the scope of the appendedclaims.

I claim as my invention:

1. A process (or converting low boiling carbons into primary conversionproducts such as ethylene and propylene olenns comprising: fiaporinngthe hydrocarbon to be converted, rapidly superheating the vapors byindirect heat exchange to a cracking temperature or 10.50 to 1100' l".for a period where the carbon to carbon linkage oi the hydrocarbon vaporstarts to nipture thoroughly admixing the superheated vapors with a heatcarrier gas maintained at a temperature above 1000' 1"., passing theresulting mixture into a reaction chamber of such volume as to permitthe time interval necessary for completing the desired primaryconversion and controlling the 'volume and temperatures of thesuperheated vapors and heat carrier gas to maintain a mean conversiontemperature in the reaction chamber such that the ratio of the tem-Pounds 0 products per 100 mm of charging stock mm Nlpllthl Heavy mannawf imam am a a o a a r n r KflU-fll'lk gal temp., F I. 100 1 1m 1. 1m21! 3,4! 1, 1m 1. 100 I, 100 2, 1m Vapil p.. 9 1, 1M 1, 1m 1, 1M 1,1m 1. mo 1, 113 1, 113 1,110 1, 112 Hun conversion terms, '1' 1,400 1,4) 1, 4G) 1, m 1, too 1, 501 1, 472 1, I11 1, 502 Approximate contacttime, Seconds.. l3 0. l3 0. 13 0. 13* 0. 18 0. 18 0. 18 0. 11 0. istconverslonperpam 42.0 77.4 46.2 N. 78.0 72.1 0.0 0.4 84.0 Yields,Lblllw Lbs. Charging Stock:

0.42 1.43 0.50 0.7 0.53 1." 0.87 1. 1.78 3. 64 6. 37 0. 40 7. 07 15. 5811. 01 12. 15 13. 11 10. 58 K 0.74 25.48 14. use 12.78 a. an 170 37.500.84 3.14 1.12 2.50 1.71 1.04 0.00 0.84 8.47 8. oo 1 15. 11 0. 41 13. uI. 04 11. U 15. 04 13. U 11. 57 3.01 6.84 3.15 5. 52 3.40 I. 5.05 2.700.8 4.01 0.87 5.38 0.81 4.70 2. 13.10 11 4.36 8. 27 11. 3. 47 0. 74 0.55 4. a 1k 03 10. N 3. 83 58. 02 2. 57 53. l) 30. 45 31 01 I7. 10. 1310. 01 15. 90 3.24 1.00 1.73 0. 11.84 3.1!) 1.50 1.50 1.50

100. 00 me (I) 100. M 11!). (IL 10). M 100. M 1m. on 10a no no. (I!

1 A11 mawili boiling above pentene.

! 'lotal distillate irom crude oil distilled to 572 F. undc 15 mm.absolute pro-ore and represents %by volume at the crude oil.

The next set of data shows the influence of conversion temperatures andstocks upon the ultimate yields of ethylene and the aromatics, (benaene,toluene, and xylenes) obtained by recycling operations, when using aheat-carrier gas temperature of 2100 1". and reaction time of 0.13second. The recycle stock consisted of all conperature diflerentialbetween the temperature of 70 the heat carrier gas and the meanconversion temperature and between the mean conversion temperature andthe temperature oi. the superheated vapors beiore admixture is between1:1 and 2:1 to eilect conversion by heat only. shock chilling theconversion products before a substantial amount of secondary reactiontakes place to a temperature at which no further conversion 'can occurand separating and collecting the reaction products.

2. The process defined in claim 1 for the production of oleflnes inwhich the hydrocarbons being cracked have C4 or less carbon atoms to themolecule and are superheated to a temperature where the carbon-to-carbonlinkages of the hydrocarbon molecule have started to rupture.

3. The process defined in claim 1 for the production of oleflnes inwhich the hydrocarbons being cracked have C5 and higher carbon atoms tothe molecule and are superheated to a temperature where substantialcracking to form primary products only occurs before mixing thehydrocarbons with heat-carrier gas, and holding the vapors in contactwith the heat carrier gas for less than 0.15 second.

4. The process defined in claim 1 in which the heat-carrier gas issuperheated steam.

5. The process defined in claim 1 forthe production of butadiene andethylene from cyclohexane wherein the vapors are superheated to atemperature above 1100 F. and the superheated vapors are cracked withsuperheated steam maintained at a temperature of approximately 18001".

WILLIAM O. KEELING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,428,311 Adams Sept. 5, 19221,811,195 Watson June 23, 1931 1,842,321 Sachs Jan. 19, 1932 1,847,238Frey et a1. Mar. 1, 1932 1,847,239 Frey et a1. Mar. 1, 1932 1,892,534Rembert Dec. 27, 1932 1,900,739 Schmidt et a1. Mar. 7, 1933 1,928,494Irwin Sept. 26, 1933 1,981,144 Held Nov. 20, 1934 2,113,536 Grebe Apr.5, 1938 2,129,269 Furlong Sept. 6, 1938 2,174,288 Klein et a1. Sept. 26,1939 2,176,453 Clark Oct. 17, 1939 2,207,552 Putt July 9, 1940 2,371,147Burk Mar. 13, 1945 2,377,847 Allen June 12, 1945

1. A PROCESS FOR CONVERTING LOW BOILING HYDROCARBONS INTO PRIMARYCONVERSION PRODUCTS SUCH AS ETHYLENE AND PROPYLENE OLEFINS COMPRISING:VAPORIZING THE HYDROCARBON TO BE CONVERTED, RAPIDLY SUPERHEATING THEVAPORS BY INDIRECT HEAT EXCHANGE TO A CRACKING TEMPERATURE OF 1050* TO1100*F, FOR A PERIOD WHERE THE CARBON TO CARBON LINKAGE OF THEHYDROCARBON VAPOR STARTS TO RUPTURE THOROUGHLY ADMIXING THE SUPERHEATEDVAPORS WITH A HEAT CARRIER GAS MAINTAINED AT A TEMPERATURE ABOVE1800*F., PASSING THE RESULTING MIXTURE INTO A REACTION CHAMBER OF SUCHVOLUME AS TO PERMIT THE TIME INTERVAL NECESSARY FOR COMPLETING THEDESIRED PRIMARY CONVERSION AND CONTROLLING THE VOLUME AND TEMPERATURESOF THE SUPERHEATED VAPORS AND HEAT CARRIER GAS TO MAINTAIN A MEANCONVERSION TEMPERATURE IN THE REACTION CHAMBER SUCH THAT THE RATIO OFTHE TEMPERATURE DIFFERENTIAL BETWEEN THE TEMPERATURE OF THE HEAT CARRIERGAS AND THE MEAN CONVERSION TEMPERATURE AND BETWEEN THE MEAN CONVERSIONTEMPERATURE AND THE TEMPERATURE OF THE SUPERHEATED VAPORS BEFOREADMIXTURE IS BETWEEN 1:1 AND 2:1 TO EFFECT CONVERSION BY HEAT ONLY,SHOCK CHILLING THE CONVERSION PRODUCTS BEFORE A SUBSTANTIAL AMOUNT OFSECONDARY REACTION TAKES PLACE TO A TEMPERATURE AT WHICH NO FURTHERCONVERSION CAN OCCUR AND SEPARATING AND COLLECTING THE REACTIONPRODUCTS.